Just did a test at non- boss dummy to check how does mastery buff effect.333 avg ilvl 20 expertise %16 miss rate against 85 %15 crit and 1337 haste and %20 main gauche chance (16+4 2.33 mastery)
2.6 axe and 1.8 offhand dagger.
So I can say buff did indeed effect some dps, pre patch damage percentage of mg was around 1.5-1.8.Im thinking with better gear (unfortunately I couldnt copy a raid premade) main gauche has some potential, but again, as adressed on a post above it might become the new ArP.
At this point, the thing we need is poison crit chance scaling with melee crit chance.It would be a major overall buff.